A power conversion device is downsized by integrally constructing a power conversion module and a control circuit board. The power conversion device includes a power conversion module 11, a control circuit board 21, and a heat sink 12. A case is divided into a module case 13 and a control circuit case 23. In a power conversion module section 10, the power conversion module 11 is thermally coupled to the heat sink 12 and contained in the module case 13 with a radiator fin 12a exposed to outside, one side of the case 13 being open. In a control circuit section 20, the control circuit board 21 is contained in the control circuit case 23, one side of the case 23 being open. Opening sides of the module section 10 and the circuit section 20 are opposite each other, and between which a heat insulating partition wall 30 is inserted.